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OBC DIVISION B · PART 9 · SECTION 9.20 — MASONRY AND ICF WALLS NOT IN CONTACT WITH THE GROUND

What are the Ontario Building Code rules for above-grade ICF walls in houses?

Part 9 gives prescriptive rules for flat-wall insulated concrete form (ICF) construction above grade in houses: minimum concrete core thickness and strength, tabulated reinforcement, and limits on wall height, openings and storeys. Waffle- and screen-grid ICFs, or walls beyond the limits, require engineered design.

Code reference
Above-grade ICF walls in Part 9 buildings may be built prescriptively where they are flat-wall systems within tabulated limits for concrete core thickness, concrete strength, reinforcement size and spacing, wall height and supported loads. Requirements also address connection to floors and roofs, framing of openings, and protection of the foam, including interior thermal barrier coverage. Configurations outside the tables need Part 4 design.
OBC Division B, Section 9.20.

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

ICF is attractive in Ontario for its combined structure, insulation and air barrier, but the Part 9 tables are narrower than marketing suggests: they cover flat cores of standard thicknesses in typical one- and two-storey loading, with reinforcement selected from tables rather than left to the installer. Common compliance issues include unsupported tall gable ends, oversized openings without engineered lintel reinforcement, and forgetting that interior foam faces need a thermal barrier such as 12.7 mm drywall. Bracing during the pour and consolidation of concrete are quality items inspectors increasingly ask about.

Plain language

ICF walls are foam blocks stacked like Lego and filled with reinforced concrete, and the code lets you build a typical house this way using standard tables for core thickness and rebar. Unusual shapes, big openings or grid-style foam systems need an engineer, and interior foam must be covered with drywall.

Related questions

How must brick veneer be supported and tied to a house in Ontario?How thick do above-grade masonry walls have to be in Ontario?

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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.